From: Jim C. Nasby <jim@nasby.net>
To: Heikki Linnakangas <heikki@enterprisedb.com>
Cc: Michael van Rooyen <mvanr@bigfoot.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Kernel cache vs shared_buffers
Date: Sat, 12 May 2007 11:55:41 -0500
Message-ID: <20070512165540.GD52939@nasby.net> (raw)
In-Reply-To: <4645CF1D.1030309@enterprisedb.com>
References: <00b301c79486$1c54da80$0200a8c0@saturn>
<4645CF1D.1030309@enterprisedb.com>
On Sat, May 12, 2007 at 03:28:45PM +0100, Heikki Linnakangas wrote:
> >In the case of it being disk-block based, my
> >inclination would be to let the kernel do the buffering. In the case of
> >the cache being table-row-based, I would expect it to be much more
> >space-efficient and I would be inclined to give the memory to the pg.
> >In that case, is it feasible to set shared_buffers to something like
> >500000 x 8k blocks? We make extensive use of indexes on the larger
> >tables and would seldom, if ever, do sequential scans.
>
> A common rule of thumb people quote here is to set shared_buffers to 1/4
> of available RAM, and leave the rest for OS cache. That's probably a
> good configuration to start with.
If you really care about performance it would be a good idea to start
with that and do your own benchmarking. Much of the consensus about
shared_buffers was built up before 8.0, and the shared buffer management
we have today looks nothing like what was in 7.4. You might find that
shared_buffers = 50% of memory or even higher might perform better for
your workload.
If you do find results like that, please share them. :)
--
Jim Nasby jim@nasby.net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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To: pgsql-performance@postgresql.org
Cc: jim@nasby.net, heikki@enterprisedb.com, mvanr@bigfoot.com
Subject: Re: Kernel cache vs shared_buffers
In-Reply-To: <20070512165540.GD52939@nasby.net>
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